A gasoline engine operates on the principle of internal combustion. A fuel/air
mixture is pulled into a cylinder, the cylinder is then closed off and the piston
is thrust upward to create compression. A spark is then introduced to ignite the
mixture to create combustion necessary to thrust the piston downward in the engine
block. There are a number of pistons inside an engine depending on the design, 4
to 12 cylinders usually. The pistons are connected to a crankshaft through a connecting
rod. Pistons fire consecutively to rotate the crankshaft inside the engine block.
The oil pump pushes oil through the
oil filter and then
supplies oil to vital engine parts including the crank and
camshaft, cylinder
walls and piston rings, valve train, cam lifters and the timing gears or chain.
Motor oil is used to lubricate and cool internal engine parts. Oil is pumped up
through the engine, then returns to the bottom of the engine and is gathered in
the oil pan. Motor oil is used to lubricate and cool internal engine parts.
The cylinder head is connected to the top of the engine block and allows the
air/fuel mixture and exhaust into and out of the cylinder block. The cylinder head
has the duty of holding the air/fuel mixture charge inside the cylinder as it is
combusted, forcing the piston downward. The cylinder head is connected to the engine
block using head bolts and using a head gasket to seal both parts together.
Overhead Cam Cylinder Head
A camshaft is used to open and close intake and exhaust ports by using valve
train components. These components will vary depending on the design of the engine.
There are primarily two styles of valve systems: "overhead cam" which consists of
a camshaft and follower/rocker arm, and the "in block" system which consist of a
camshaft, lifter, push rod, rocker arm. Both styles utilize a valve spring to hold
the valve closed.
Car Acceleration
Acceleration is the process of changing the rate of velocity or movement. This
is the result of available power from the engine. Usually, the bigger the engine,
the power it makes. However, a turbo
charged or supercharged (forced induction) engine provides an exception to the
rule. When air is forced into an engine using a turbo/supercharger it can produce
more power and improved acceleration with a smaller engine. Whenever you hear someone
mention horsepower the first thing that usually comes to mind are cars; fast cars
with extreme torque, muscle cars with lots of power, and vehicles capable of extreme
speed. But why is horsepower so important? James Watt, a famous 19th century engineer,
created the term "horsepower" in 1782 as he improved the power of the steam engine.
While watching horses haul coal out of a coal mine he came up with the idea of
defining the power exerted by these animals, thus the term "horsepower" was born.
He calculated that a normal horse attached to a mill that ground corn or cut wood
walked in a circle that was 24 feet in diameter. He then calculated that the horse
pulled with a force of 180 pounds. Watt noticed the horse could make 144 trips around
this circle in an hour. That is 2.4 trips per minute. Using these numbers he calculated
that the horse traveled about 180.96 foot per minute then rounded up and came up
with 181 foot per minute.
He then multiplied the 181 foot per minute by 180 pounds of force the horse exerted
and came up with the number 32,580 foot pounds per minute then rounded up again
to the number 33,000 foot pounds per minute. This number is equal to one horsepower.
Mr. Watt used his new term to rate the power of the steam engine. Since most people
were unfamiliar with the steam engine he had to come up with a comparison measurement
that the farmer of the day would understand. As with any measurement there are different
variations and different methods of measuring horsepower or hp. The normal measurement
of horsepower is called mechanical horsepower.
Engine Compression
In a vehicle there are hundreds of moving parts that get you from the point A
to point B. The modern automobile is an intricate piece of machinery and a wonder
of the technological processes. One of the main processes that produces a vehicle's
power is called compression. Compression is the pressure of the air/fuel mixture
that has been compressed in the cylinder of the engine by the piston. As the piston
travels upward this mixture is compacted down into a smaller volume so it can be
ignited by a spark plug. In a four stroke engine compression occurs on the upward
stroke or the upward push of the piston through the cylinder bore before the
spark plug ignites the mixture.
Checking Compression
To check compression you must first disable the
ignition system to keep the
engine from starting. Locate the ignition coil and disconnect it, or unplug the
ignition module connector. To test if the ignition is disabled crank the engine
over, the engine should not start.
With the engine warm remove one of the spark plugs and insert the
compression tester into the
spark plug hole. Now turn the key of the engine for at least 5 to 10 seconds to
get an accurate reading. Repeat this for each cylinder of the engine and record
your results relating the reading to the individual cylinder. If the individual
readings vary by more than 10% between cylinders you may have a problem.
Optional compression testing methods include an electric starter tester. This
test measures the battery amperage draw to each cylinder while the engine is cranking.
It will show you which cylinders have good compression and which have the least
compression. In a gasoline engine a moderate compression ratio is needed, around
140 to 160 pounds per square inch. Each manufacturer produces specific compression
ratios for their engines to closely control the power output and emissions. If high
compression exists it can cause a problem known as pre ignition or detonation. A
compression test can detect internal combustion malfunctions such as, bad valves,
bad piston rings, or excessive carbon build up. These problems if left un-repaired
can cause more extensive engine damage and even catastrophic failure.
Octane Rating
Why should you read the octane rating at the gas pump? The compression ratio
of your engine determines the octane required for optimum performance. The octane
rating of gasoline states the level fuel that can be compressed before it ignites.
Under extreme conditions such as heavy acceleration fuel can ignite without the
use of the spark plug resulting in a "ping" or "pinging" and under ultra heavy condition
a knocking sound. When this condition is left un-treaded it could result in sever
engine damage.
The compression ratio is the number that can be used to help predict the engine
performance. It is calculated by taking the volume of the cylinder, when the piston
is at the bottom of its stroke, and then dividing it by the volume when the piston
is at the top of the stroke, the higher the compression ratio the more power your
engine can produce, The extra power produced is coupled with added efficiency in
turn help improve gas mileage.
(Note: most vehicles automatically adjust for different octane levels.)
How Engine Horsepower Works
Whenever someone mentions horsepower the first thing that comes to mind is cars.
Fast cars with extreme torque, vehicles with large power and extreme speed. But
what makes horsepower measuring so meaningful? And why is it called horsepower?
The word horsepower was created in 1782 by James Watt, a famous 19th century engineer
while he was developing a way to improve the power of a steam engine. While watching
horses haul coal out of a coal mine he came up with the idea of defining the power
exerted by these animals. He calculated that a normal horse attached to a mill that
ground corn or cut wood walked in a circle that was 24 feet in diameter.
He then calculated that the horse pulled with a force of 180 pounds. Watt
noticed the horse could make 144 trips around this circle in an hour. That is 2.4
trips per minute. Using these numbers he calculated that the horse traveled about
180.96 foot per minute then rounded up and came up with 181 foot per minute. He
then multiplied the 181 foot per minute by 180 pounds of force the horse exerted
and came up with the number 32,580 foot pounds per minute then rounded up again
to the number 33,000 foot pounds per minute.
This number equals one horsepower. Mr. Watt used his new found term to rate the
power of the steam engine. Since most people were unfamiliar with the steam engine
he had to come up with a comparison measurement that the normal farmer of the day
would understand. As with any measurement there are different variations and different
methods of measuring horsepower or hp. The normal measurement of horsepower is called
mechanical horsepower.
Metric Horsepower
In Europe horsepower is measured a slightly different way. Horsepower is known
by the various countries literal translation of the word horsepower. Some acronyms
include PS, CV, pk and so on. Depending on the origin of the engine in question
its horsepower is measured by that country's standards. Metric horsepower is defined
as .73549875 kW. This is roughly 98.6% of mechanical horsepower.
Horsepower in Europe
Other countries have their own ways to measure horsepower. PS stands for Pferdestarke
or horse strength. This is the German equivalent of horsepower. It is no longer
used in Germany but it is in some other counties. It has since been replaced by
the kilowatt but the EEC where horsepower was still used in advertisements as most
people do not know the use of the kilowatt as a power measurement for combustion
engines. Mathematically a PS = .73549875 kW = 0.9863201652997627 hp. The Dutch have
the paardenkracht (pk). The Swedish have the hastkraft (hk).
The Finnish have the hevosvoima (hv). All of these are equal to the German (ps).
RAC horsepower, or taxable horsepower, is a British standard measurement of an automobile's
power. It was adopted by the Royal Automobile Club. Taxable horsepower does not
reflect true horsepower but it is a calculation based on the engine's bore size,
the number of cylinders and a presumption of engine efficiency.
The figure is no longer used as a standard in the UK but it is still put to use
for the calculation of a vehicle's tax. The equation is RACh.p.= D squared * n/2.5
where D is the diameter of the bore of the cylinder in inches and n is the number
of cylinders.
How Horsepower is used Measure the Power of an Engine?
There are several names used to give an idea on how powerful an engine is. They
are Nominal horsepower, Indicated horsepower and SAE gross horsepower. Nominal horsepower
(nhp) is an early 19th century standard for estimating the power of steam engines.
NHP = 7 x area of the piston x equivalent piston speed/33,000. It is measured by
the size of the engine and the piston speed. Indicated horsepower (ihp) is calculated
from the pressure in the cylinder. It is a misleading measurement as the actual
power may be 79% to 90% of the indicated power.
This was used to measure steam engine power. This measurement was open to interpretation
so numbers varied. SAE gross horsepower was used by most car makers prior to 1972.
It was measured with a test engine that had no accessories attached. It was a measurement
of the maximum value of the engine and was often over rated to influence the sales
of muscle cars. An engine that has its horsepower rating approved by the SAE will
always be true to its number.
Common Problems:
Neglected regular
maintenance resulting
in premature engine failure
Cooling system neglect causing
overheating resulting
in premature engine failure
Proper maintenance is crucial to optimum performance for every internal combustion
engine. Follow your manufacturers recommended service schedules. Protect yourself
by servicing your car regularly.
There are four main sections to the internal combustion engine.
Engine Block: (short block) note: a long block includes cylinder
heads.
a. main engine block
b. crankshaft
c. pistons
d. piston rings
e. connecting rod pin
f. connecting rod
g. camshaft (in
over head valve engines)
h. lifters (in
over head valve engines)
i. oil pump
j. oil pump drive
k. oil pump pick up
l. gaskets and seals
m. freeze plugs
n. oil pan
o. assorted bolts
p. timing chain
Cylinder Heads
a. main head cylinder body
b. intake and exhaust valves
c. valve keepers
d. valve spring
e. valve spring retainer
f. valve stem seal
g. camshaft (overhead
cam only)
h. cam followers
(overhead cam only)
